US2050149A - Television - Google Patents

Description

1936- H. SBAIRD 1 2,050,149

TELEVI S I OH Filed May 29, 1929 2 Sheets-Sheet 2 Patented Aug. 4, 1936 UNITED STATES INS-0,149

. TELEVISION Hollis S. Baird, Boston, Mass., assignor to Shortwave & Television Corporation, Boston, Mass, a corporation of Delaware Application May 29, 1929, Serial No. 366,974

5 Claims.

This invention relates to television and particularly to apparatus for receiving transmitted television pictures although in certain of its aspects the invention is also applicable to the. transmission of such pictures. I

The present-day television receiving apparatus is considered bulky and diflicult to operate except by an experienced person and has many objectionable features.

One of the objects of the present invention is the provision of a television receiving apparatus which is small and compact and it is similar in its physical dimensions to a small table-mounted radio broadcast receiving set, so that it can be contained in a small cabinet which may be given an artistic appearance to harmonize with the furnishings of a room, thus to avoid any of the features which have heretofore prevented the known television apparatus from becoming a common and widely used product.

The present-day television transmitting stations usually employ scanning discs which scan successive portions of the picture to be transmitted. The scanning disc has a plurality of scanning apertures or windows which are spaced in a spiral line about theperiphery of the disc. The receiving apparatus must have a scanning device that has scanning windows arranged in the same order as in the transmitting disc. The scanning discs of the various television transmitting stations are not standardized and the various stations may, and many do use, scanning discs having different systems of windows. Thus, at the receiver, it may be necessary to provide as many scanning discs .as there are difierent systems of scanning windows and to change from one scanning disc to another when it is desired to shift reception from one transmitting station to another. Not only is it necessary to change the scanning discs but it may be necessary to vary the position of the disc-with regard to the view window, or the window in which the received picture appears. Such changes. usually require an elaborately designed apparatus and necessitate the use of tools to effect the changes. The present-day apparatus thus is considered commercially unsuitable and its operation .is quite beyond the skill of the average. household.

It is an object of the present invention to provide a television receiving apparatus and a type of scanning device therefor so arranged that the apparatus can be quickly adjusted by an unskilled person to receive transmitted television signals from different transmitting stations using difl'erent systems of scanning windows.

Unless the scanning device at both the transmitting and receiving stations are started on the same window, or in phase, the picture at the receiving end will be out of frame, that is, the lower half of the picture may be in the upper .5 portion of the view window, and the upper half of the picture may be in the lower half of the view window.

Heretofore, a common method of bringing the picture into frame has been by restarting'the receiving apparatus a sufiicient number of times to catch the proper scanning window or by throwing the receiving apparatus out of synchronismrwith the transmitting apparatus and either speeding up or slowing downthe receiving apl5 paratus until the picture is in frame and then holding it in synchronism. Such a method of operation is considered entirely unsuited for successful commercial use in the average household. Consequently, an object of the present invention is to provide means for bringing an out-of-frame picture into frame in a very simple manner and without either de-energizing the driving motor or throwing it out of synchronous speed.

i The present-day .television receiver usually employs as a source of illumination an electric lamp or tube containing within a transparent envelope a conductinggas', generally neon, and spaced electrodes at least one of which is in the form of a plate. The characteristic feature. of the tube is that theplate glows or is surrounded with a luminouslayer of the conducting gas when the electrodes are energized at a suitably high .direct current potential; and the intensity of the illumination of the luminous layer varies in proportion to the impressed voltage. The intensity of illumination of the luminous gas ordinarily is low so that the received picture is not brilliantly illuminated, especially as thescanning windows. through which the light passes are very minute.

Consequently, it is an object of the present invention to increase the illumination of the receive-d picture from a gaseous tube of the above type by employing a tube having a plate or electrode that is considerably larger than the dimensions of the received picture and condensing the light from the plate into a smaller but more intense beam, thereby increasing the illumination of the received picture.

The light emitted from the neon tube is red in color. Consequently, the received picture has the same coloryand this color is considered ob- ,iectionable by many. I have found that the color of the picture can be modified and made something different than that given off by the source of illumination by interposing one or more suitably colored transparent screens between the tube and the displayed picture, thereby providing a received picture the color of Which is different from that of the source of illumination; and this constitutes a further object of the invention.

Another object of the invention is the provision of a scanning device which consists essentially of an endless flexible belt containing the scanning windows. By the provision of the belt the apparatus can be greatly reduced in dimensions over those necessary with the usual scanning disc; and belts having different systems of scanning windows can be substituted one for another by an unskilled person without trouble and the use of tools.

A further object of the invention is the provision of a scanning belt composed of transparent material as celluloid and the like coated on one side with a light sensitive emulsion or film and wherein the view windows are photographed on the film by subjecting the emulsion to a source of illumination except at the location of the windows so that when the emulsion is subsequently developed and fixed the belt is opaque except at the windows, where it is transparent. A preferred form of belt consists of a section of standard moving picture film wherein the windows are photographed on the belt.

A further object of the invention is generally to improve the construction and operation of television apparatus and particularly television receiving apparatus.

Fig. 1 is a front elevation of a television receiving apparatus embodying the present invention.

Fig. 2 is a plan view of the receiving apparatus contained within the casing of Fig. 1, the enclosing casing being shown in section.

Fig. 3 is a front elevation of the apparatus of Fig. 2.

Fig. 4 is a sectional detail taken along line 44 of Fig. 2, and illustrating especially the optical system of the apparatus. 1

Fig. 5 is a sectional detail of the belt tightener taken along line 5-5 of Fig. 2.

Fig. 6 is an enlarged sectional elevation of the scanning belt.

The apparatus herein shown includes a base plate ID on which the component parts of the apparatus are supported and the enclosing casing l2 which is mounted on and is removably secured to the base and encloses the various parts of the apparatus. The essential feature of the apparatus, which is mainly responsible for the compact overall dimensions of the apparatus and for many of the other advantages thereof, includes a narrow scanning belt Id of suitable dimensions which is passed over the supporting pulleys l5, I8, 20 and 22 which are carried by the base I 0 and are arranged in rectangularly spaced relation and are rotated about vertical axes.

The pulleys I 8, 29 and 22 are or can be identical and each can have the slightly crowned beltreceiving face 24, see Fig. 5, and the radially-outstanding edge-fianges 26, or at least a lower flange to hold the belt on the pulleys. The pulleys I 8 and 22 are rotatable on stud shafts 28 which are fixed in Vertically upstanding bosses 36 carried by the base plate ID. The pulleys are restrained removably on said stud shafts by screws 32 which are removably threaded in the upper ends thereof and have washers 34 that overlie the top faces of the hubs of said pulleys.

Means are provided to maintain the scanning belt taut. To this end, the pulley 20, see Figs. 2 and 5, is journalled on the vertical stud shaft 3'6 which is carried by a boss 38 at the similar ends of horizontal arms 49. Said arms at their other ends are provided with a vertical boss 42 which is supported on a vertical shaft 44 carried by the bracket 46. A tensile spring 48 is connected with and is extended between one of said arms 40 and a projecting arm 59 of said bracket 46 whereby to urge said pulley 20 constantly against the belt, thereby to maintain it taut.

As has been previously stated, pictures are transmitted by scanning discs employing different systems of scanning windows so that a belt adapted for one system cannot receive pictures transmitted by another system. Thus, the belts having various systems of scanning windows will be of varying lengths. Means are herein provided to accommodate belts of various lengths so that one belt can be replaced by a belt having a different system of scanning windows thereby to condition the apparatus ready to receive pictures transmitted under different systems of scanning windows. To this end, the bracket 46 which supports the belt tightener pulley 20 is independent of the base l0 and has a horizontal foot 52 which rests upon said base. Said foot has a plurality of spaced apertures 54 arranged in line thereon and said base has a pair of upstanding attaching screws 56 which can enter any two consecutive apertures. Thumb nuts 58 are threaded on Said screws and serve to clamp the bracket detachably to the base. Thus, by positioning the bracket so that the attaching screws are within a selected pair of consecutive apertures, belts of various lengths, having varying systems of scanning windows, can be supported by the pulleys, the apertures being so spaced that they correspond with belts of certain lengths.

The pulley I6 constitutes the driving pulley of the belt and has peripherally-outstanding gear teeth 80 at the top and bottom edges thereof which constitute driving sprockets for the belt. The belt has a plurality of longitudinally spaced tooth-receiving apertures 62 which are arranged in parallel lines adjacent the upper and lower margins of the belt with which the driving teeth mesh. The pulley I 6 is driven at appropriate speed by a motor 64 that preferably is a synchronous motor and is operated at such speed that the rate of movement of the scanning apertures in the belt is maintained in synchronism with the rate of movement of the scanning apertures in the transmitting scanning device, so that the receiver will stay in synchronism or step with the transmitter without unusual adjustment.

The motor drives the pulley [6 through mechanism by which the received picture may be brought into and maintained in frame when it is out of frame. To this end, the motor drives a spiral gear 66 which preferably is sufiiciently long so that the teeth on the gear make one revolution thereabout. A similar spiral gear 68 is supported in spaced parallel relation with said gear 66 and drives a bevel gear 70 which is in mesh with a driven gear I2 fixed to the hub 74 of the driving pulley I6. The bevel gears 70 and 12 are of different pitched diameters so that the speed of the pulley I6 is suitable for the purpose. The motor herein shown has a synchronous speed of 1,800 R. P. M., and the bevel gear 10 thus is iarger than the bevel gearflZ so that the pulley 16 can .be driven at a sufficiently greater rate of speed than the motor. The two spiral gearszfifi and -.6.8 are operatively connected by means of an interposed spiral idler gear 16. Said idler gear ismovable .axially of said spiral gears 56 and 68 and to this end, is rotatably :supported on a 'shaft 18 which is slidable in a bracket 88 but is -heldagainst rotation. The forward end of said shaft 18 is provided with external screw threads '82 and is threaded into an internally screwthreaded and axially-aligned passage '84 in the hub 86. Said hub is rotatably-supported in the casing l2 and is held from axial movement by fixed fingers 88 which project into a continuous peripheral groove 90 in said hub. Said hub is extended outwardly through said casing and is terminated in a knob 94 by which the hub can be rotated. It is apparent that by rotating the hub the shaft 18 and consequently the idler gear 16 will be moved axially of said gears 66 and 68, 'while maintaining its driving engagement therewith. The position of said gear 16 with relation to said gears 66 and 68 determines the angular position of the pulley I6 with regard to the driving shaft of the motor since the axial move- -ment of the idler gear serves to catch the gear 68 with respect to the gear 66. Thus, by varying the position of the idlergear the relative angular positions of the pulley [6 may be shifted while the apparatus is in operation, thereby 'varying the position of the belt andbringing outof-frame pictures into frame. The length of the spiral gears 65 and 68 is preferably such as to shift the picture either forwardly or 'backwardly at least by the distance of one-half a frame or the width of one picture.

The optical system includes a gaseous conduction tube, as the neon tube 96, which is removably located in the supporting socket 98 within the area bounded by the belt. The tube has spaced plate electrodes I and I02, of which-the electrode I00 is the source of light. Said electrode is here shown as approximately square and is considerably larger than the dimensions of the received image. The light from said electrode is concentrated onto the belt so that the 'unit intensity of illumination of the picture can be greater than that of the electrode. To this end, condensing lenses I04 are mounted in a barrel I06 secured removably to an upstanding supporting bracket I08 and interposed between the light source and the belt I 4. Said lenses serve to condense or concentrate the light from said electrode I00 and to project a beam of more intense light upon the belt.

A viewing tube H0 is located immediately in front of the belt and the condensing lenses and is supported removably on a bracket H2 carried by the base Ill and located in front of the front wall of and in a vertical slot in the enclosing casing I2. Said tube H0 has a tapered passage therein which terminates adjacent the belt in a square or rectangular view opening or window H4. An enlarging lens H6 is located in said tube in front of the View window and serves to enlarge the picture formed at said opening.

The belt is formed with a plurality of minute and preferably rectangular scanning windows H8 which pass light from the light source into the view tube, the remainder of that portion of the belt which is visible through said view window being relatively opaque. Said scanning windows are arranged in spaced order lengthwise along the length-of the belt and each window is :lower than the :next adjacent upper window. Thus, :each window in succession as it passes across the view window gives illumination, the intensity of which is .varied by the intensity of illumination of the A tube '96, which illumination is varied by the in coming television signals that impress a variable voltage on theelectrodes of the tube. Thus, when all of, the scanning windows, from the uppermost to the lowermost window, havepassed in succession across the view window, one complete picture will have been received. Dueto the persistence of vision, the impression recorded in the eye of the observer .by the passage of the uppermost scanning window will persist until after the passage of the lowermost window, thus creating the impression of a picture all parts 01' which are presented simultaneously. Obviously, the number of windows in the belt must correspond with the number of windows in the scanning device of the transmitting apparatus and thesewindows must pass simultaneously into and out of operative position. 1

. A further advantage of the scanning belt over 7 the scanning disc is that the scanning windows of the belt move in straight parallel lines whereas the scanning apertures :ofthe disc moveincircular paths so that the picture has sensibly-arcuate top and bottom edges instead of thegenerally den sired straightedges unless the scanning disc has a relatively great diameter at the apertures.

While, for some purposes, the scanning belt .canbe of any suitable material, as a thin metal belt, wherein the windows appear as perforations therein much superior results areobtained when the belt is made of a flexible transparent material, as celluloid, or other cellulose ester, and particularly when the belt is composed of a :section of moving picture film. The particular scanning I belt herein shown is composed of an endless section of moving picture photographic film wherein the celluloid or the like body of the .belt .is-transparent and has on one face thereof a light sensitive emulsion film I25). shown in Fig. 6, in greatly enlarged thickness. The scanning windows 8 are photographed on the film. This is conveniently done by focusing a camera with the film therein upon a black backgroundthat has a white surface, as a white square target thereon.

the dimensions of the target being proportional to the size of the windows. The adjustment of the camera is such that the dimensions of the image of the target is reduced on the film sufliciently to produce a window of proper dimensions, the specific window herein shown being fifteen thousandths of an inch square. After each exposure, the film is moved forwardly one frame and the target is moved downwardly a dis tance suitable to properly locate the next succeeding window on the film. The lens of the camera, can be moved transversely of the film instead of the target to the same end. This operation is repeated until the desired number of windows are photographed. There are 48 windows in the particular belt herein shown and the belt has a length of three feet. The photographic film is then developed and fixed, and the resulting negative gives a series of opaque black sections on a. transparent background. Positive films are printed from this negative and provide an opaque background with transparent windows, which is what is desired. A scanning belt so prepared has many advantages. By photographically reducing the dimensions, the minute win- 7 dows can all be uniform and shaped to accurate dimensions from a master, or target, that is relatively large and need not be made accurately to any particular dimensions. Once the negative has been made, positives that are intended for use with the above described apparatus can be cheaply made photographically so that the cost of a belt is relatively small. Furthermore, the belt is free from small perforations in which dust and lint can accumulate, thereby to destroy the sharpness of definition of the picture. The belt is placed upon the pulleys with the emulsion side outermost so that there is little danger of scratching the emulsion and thus making it transparent in spots.

The cellulosic photographic film of which the belt is composed can be obtained in a variety of colors. Consequently, the windows will be correspondingly colored. I have found that the color of the film at the windows modifies the color of light emitted by the neon tube and consequently modifies the color of the received picture. Thus, the color of the picture can be varied to suit ones taste by a proper selection of the color of the film. I find that a film having an amber color in combination with a neon tube will give a picture that is lighter in color than that of the neon tube alone and appears as a rather light orange. If, for a certain color of the displayed picture, it is desired to supplement the color of the belt with other colors, as for the production of a white light at the picture, suitably colored screens I22 may be interposed between the belt and the light source, or in front of the condensing lenses I04. In view of the necessary absorption of light by the colored belts and screens, the increase in illumination of the picture by the condensers I04 is particularly desirable.

I claim:

1. Television apparatus ncl ding an endless flexible scanning belt, driving and supporting means for said belt including a plurality of pulleys over which said belt is passed, and means to condition said apparatus to support and drive various scanning belts of various lengths including means to support one of said pulleys in any one of a plurality of operative positions that are differently spaced from certain of the remaining pulleys, whereby to vary the length of the passage about said pulleys.

2. Television apparatus including an endless flexible scanning belt, driving and supporting means for said belt including a plurality of pulleys over which said belt is passed, and means to condition said apparatus to support and drive various scanning belts of various lengths, including means to support one of said pulleys in any one of a plurality of operative positions that are differently spaced from certain of the remaining pulleys, whereby to vary the length of the passage about said pulleys, and means to maintain a taut belt on said pulleys.

3. The method of making a scanning device for television purposes, wherein the device has a light-sensitive photographic-negative which consists in taking on such negative successively-displaced features of a light target on a dark background, progressively displacing the negative and also the target in a direction transverse to the line of displacement of said device prior to the taking of such picture, and developing the negative, wherein the target and the dark background appear as contrasting dark and light regions.

4. The method of making a scanning device for television purposes, wherein the device has a light-sensitive photographic-negative which consists in taking on such negative successively-displaced pictures of a light target on a dark background, progressively displacing the negative and also the target in a direction transverse to the line of displacement of said device prior to the taking of such pictures, and developing the negative, wherein the target and the dark background appear as contrasting dark and light regions, and photographically-printing a positive from such negative, wherein the pictures of the target appear as transparent localities on an opaque body.

5. The method of making a scanning screen, which comprises applying a light sensitive coating on a transparent sheet, exposing a portion of the sensitized sheet to impress thereon the image of an object, eflecting a predetermined relative movement between the sheet and the object, again exposing a portion of the sensitized sheet so that another image of the object is impressed thereon, repeating the steps of elfecting the relative movement between the sheet and the object and exposing portions of the sensitized sheet so that a series of objects is impressed on the sheet, and developing the sheet to render the coating opaque with the images appearing thereon as transparent areas.

HOLLIS S. BAIRD.

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